Because many pipe installations are subjected to sizeable temperature and pressure variations, it is frequently necessary to provide pipes, ducts and the like with one or more expansion joints to accommodate the pipe growth, shrinkage or displacement.
One approach to solving the problem of providing compensation for separative thrust at expansion joints is exemplified in my own earlier U.S. Pat. No. 4,018,463, issued Apr. 19, 1977. In my earlier patent, the compensating portions are all encased in a large outside cylindrical portion having a maximum diameter appreciably larger than the pipe diameters which the coupling is intended to join. Large annular members are also provided within the cylindrical portion. Articulating connections attached to the annular members are located within the space enclosed by the cylindrical portion, and thus could not be got at for repair or replacement without first entirely disassembling the pipe joint by removal of the cylindrical member. In the embodiments disclosed in my earlier U.S. Pat. No. 4,018,463, such disassembly could not take place while the pipe remained filled with liquid or fluid under pressure, because the cylindrical portion was a pressure-containing member, and its removal would have allowed liquid or fluid to escape from the pipes.
It is now proposed to take a different approach to thrust compensation for expansion pipe joint couplings in which the compensating members are located entirely outside of the expansion pipe joint. Prior art pertinent to this particular approach includes U.S. Pat. No. 2,545,701, McCausland, issued Mar. 20, 1951 and U.S. Pat. No. 3,458,219, Wesch, issued July 29, 1969.
The McCausland patent illustrates the provision of a bellows-like expansion joint, together with a plurality of exteriorly mounted thrust compensating devices, one of which includes a cylinder connected to one pipe end and a piston within the cylinder connected to the other pipe end. The volume within the cylinder on one side of the piston is adapted to be pressurized with the fluid contained in the pipes themselves, and this pressure seeks to cause relative movement between the piston and the cylinder which would compensate for the separative thrust on the expansion joint.
In the Wesch patent, tne compensation is brought about by way of tension coiled springs connected between flanges attached to the pipe ends, and a telescoping cylindrical member is provided between the pipe ends to allow the expansion itself to take place.
In the McCausland prior patent, the structure of the thrust-compensating means is not such as to permit the pipe ends to undergo anything but axial displacement with respect to each other, without the risk of binding arising within the piston/cylinder combination. This is so because the piston and cylinder are mounted rigidly with respect to the pipe ends, and any articulation of the pipe ends with respect to each other would "bend" the piston and its piston rod within the cylinder, thus causing binding. A further difficulty with McCausland is the risk of "sag" for the piston and cylinder arrangement under zero pressure, when the pipes are arranged other than vertically. Additionally, the cylinder/piston arrangement in McCausland causes the pipe flanges to be "pulled together", due to the fact that the cylinder is disposed between the two flanges. This results in two disadvantages. The first disadvantage relates to the fact that the flanges must be separated sufficiently to allow the cylinder to be inserted between them, thus establishing a minimum size for the expansion joint. The other disadvantage relates to the question of maintenance and service. In McCausaland, the external compensating cylinders must be completely removed if it is necessary to partially disassemble any of the main pipe expansion assembly. It would be an improvement to provide a thrust compensating arrangement in which access to the main expansion assembly can be had more easily due to the fact that removal of the thrust-compensating portion is simplified. Finally with respect to McCausland, it is noted that the cylinder itself is subject to both tensile stress and hoop stress when in operation. it would be of advantage to eliminate at least the tensile stress in the cylinder.
With respect to the Wesch patent mentioned above, the compensation for axial thrust arises through the provision of coil springs, which results in the disadvantage that the compensation varies with the degree of axial displacement due to the spring constant. A further difficulty is the fact that the degree of angulation permitted between the pipe ends is very restricted due to the provision of essentially cylindrical seats between the portions defining the telescoping assembly.